1. Field of Invention
The present invention relates to an imaging system and a projection apparatus. More particularly, the present invention relates to an imaging system and a projection apparatus with lower cost and better imaging quality.
2. Description of Related Art
Please refer to FIG. 1A and FIG. 1B. The conventional projector 40 comprises an illumination system 10, a light valve 20 and an imaging system 30. The illumination system 10 emits an illumination beam 10a. The light valve 20 is disposed on the optical path of the illumination beam 10a to convert the illumination beam 10a into an image beam 20a. The imaging system 30 is disposed on the optical path of the image beam 20a to project the image beam 20a unto a screen (not shown), and the imaging system 30 includes a projection lens 31 and a fixed light shutter 32. The fixed light shutter 32 is disposed in die projection lens 31. The low-intensity light in the aperture of the projection lens 31 is shielded by the fixed light shutter 32, so as to enhance the contrast.
However, because the fixed light shatter 32 is located inside of the projection lens 31, the structure of the projection lens 31 is relatively complex and the manufacturing cost is higher. Besides, the effect of enhancing the contrast is not as good as expected because the light shutter 32 can only shield off the circumferential dispersed light of the lower portion of the image beam 20a. 
To solve the undesired effect of contrast enhancement of the light shutter 32, another design of the conventional light shutter is respectively illustrated in FIGS. 1C and 1C′, and FIGS. 1D and 1D′. In FIGS. 1C and 1C′, the light shutter 32′ is formed by a plurality of leaves 32c. The contrast can be improved by opening and closing of the leaves 32c to shield off partial light beams, as illustrated in FIGS. 1C and 1C′ respectively. However, the structure of the light shutter 32′ comprising a plurality of leaves 32c is complicated, which increases the manufacturing cost. As shown in FIGS. 1D and 1D′ respectively, a movable light shutter 32″ is used for adjusting the contrast. The light shutter 32″ is formed by a half-annular shielding plate, therefore, only the circumferential dispersed light located at the upper portion of an image beam 20a can be shielded. Consequently, the effect of contrast enhancement is still insignificant. In addition, the casing of a projection lens 31 requires an opening to make a light shutter 32″ move into or away from the projection lens 31, the entire structure of the projection lens 31 is not stable. As a result, when the movable light shutter 32″ is moved into or away from the projection lens 31, the lens of the projection lens 31 (not shown) is likely to vibrate, thereby affecting the imaging quality.